i have a 2013 infiniti g37x with around 125k miles. on thursday the p1233 code came up that day and went off the next and has been off ever since until today. but now i have the P0420 code with it. it seems to run fine and but it sometimes seems to hesitate or shift hard
P1233 has to do with the electronic throttle body. You could try cleaning it with the appropriate spray cleaner in case it's sticking a bit:
P0420 usually means your catalytic converter is bad but there are other possible causes. See diagnostic information for in the links below:
https://www.walkerexhaust.com/support/tech-tips/diagnosing-catalytic-converter-p0420-code.html
https://www.carparts.com/blog/p0420-code-catalyst-system-efficiency-below-threshold-bank-1-2-2/
https://www.obd-codes.com/p0420
